I think some more information might be useful. What's the exact sequence of actions? How much time passes? Call me a skeptic, but I would think that a battery "shorting" to "dead" that quickly is likely to be pretty dramatic, and I don't see how a fast key turn could result in shunting that much current. I think there's a good chance that something else is going on.
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macDec 12 '12 at 4:00

also, an edit to the question might be in order to highlight your question...I think your question is "what is likely to be causing this behavior?"
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macDec 12 '12 at 4:02

2 Answers
2

Its not a short, it's a bad connection. Typically at the battery terminal, but maybe the main body ground off the battery or main connection at the fuse box off power side. Seen it a lot as a tech. Check for looseness or corrosion.

You answered your own question. You've got a short. Until you find and fix the short you're going to keep ruining batteries.

Edit: Turning the key in any fashion allows the current from the battery to travel throughout the car ( turning the key connects the circuit ) and reach the short that's killing batteries. If the speed at which you turn the key really does make a difference, then it's possible the short is located in the ignition switch itself. But like mac, I too am skeptical that turning the key fast or slow is significant, without more detail.